Nonreflecting coaxial line section



April 14, 1970 s. MxNlcH NONREFLECTING COAXIAL .LINE SECTION Filed oct.11, 1965 INVENTOR BYM/ I MM ,dfn- ATTQENE 5 s /M @13H INW m UnitedStates Patent O 3,506,935 NONREFLECTING COAXIAL LINE SECTION Sam Minich,Euclid, Ohio, assignor to Bird Electronic Corporation, Solon, Ohio, acorporation of Ohio Filed Oct. 11, 1965, Ser. No. 494,687 Int. Cl. H03h7/38 U.S. Cl. 333-34 4 Claims ABSTRACT OF THE DISCLOSURE A nonreflectingcoaxial line section for coupling coaxial lines to devices such as lineterminations. The subject invention is capable of coupling a coaxialline to another device such as a resistive line termination within theshortest possible axial length while maintaining a voltage standing waveratio of less than 1.20 for frequencies from direct current to 3,000 mc.This is achieved by employing tapered inner and outer conductors inwhich the taper is in the range of 20 to 40` degrees. In one embodiment,the taper is achieved by series of steps of relatively short axiallength on both the inner and outer conductors. In another embodiment,the coupling device is comprised of conical surfaces having angles inthe range of 20 to 40 degrees.

One of the problems encountered in coupling devices for coaxial lines isthat of compensating for the irregularities or discontinuities betweencoaxial sections of different diameters and diameter ratios and forcompensating for discontinuities between a coaxial line and a coaxialline device such as a line termination having a hornshaped outerconductor and a cylindrical resistive inner conductor.

It is known in the art to employ inhomogeneous sections as couplingdevices between homogeneous sections of different diameter. Attemptshave been made to ernploy a plurality of quarter-wavelength steps on theinner and outer conductor sections as transformer sections betweencoaxial lines of different diameters. One example of such use is shownin Figures 6-5, page 311 of a text entitled, Microwave TransmissionCircuits by Ragan, copyright 1948. Examples of coaxial sectionsemploying tapered inner and outer conductors are disclosed in Rose U.S.Patent 2,627,550 and an article entitled, Reflection Co-efiicient Curvesof Compensated .Discontinuities on 'Coaxial Lines and the Determinationof the Optimum Dimensions by A. Krous in the Journal of the BritishInstitute of Radio Engineers, volume 20, No. 2, February 1960, page 145.None of these disclosures, however, reveal a coaxial line discontinuitywhich is relatively short in axial dimension and which may beparticularly adapted to connect a coaxial line to a coaxial linetermination Kwithout appreciably increasing the physical dimensions 4ofhousing for the line termination.

Accordingly, it is an object of this invention to provide an improvedcoaxial line discontinuity for connecting a rst coaxial line section toa second coaxial line section or to a coaxial line device.

It is another object of this invention to produce a coaxial linediscontinuity with a minimum amount of reflection and which isrelatively short in axial dimension.

Still another object of this invention is to provide a coupling devicefor a coaxial line termination which coupling device is relatively shortin axial dimension and which produces a minimum of reflection.

Yet a further object of this invention is to provide an improved coaxialline coupling device which is simple and economical in construction,easy to assemble and contains relatively few parts.

Briefly in accordance with aspects of this invention,

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a relatively short coaxial line coupling section includes an annularouter conductor assembly having an interior surface with a mean slope inthe range of 20 to 40 and an inner conductor assembly having a Meinkestep. This particular embodiment is provided with a plurality of stepson the outer conductor and a like plurality of steps on the innerconductor each of which steps have their apices positioned alongsubstantially straight lines and with one series of steps slightlyaxially displaced relative to the other series. Preferably theprojection of the mean slope of the outer conductor intersects the axisof the inner conductor of the coaxial line or the extension of the axisof the line termination at an angle of at least 20 and in the preferredembodiment this angle is in the range of 25 to 40. Further, the steps onthe outer conductor assembly constitute equal increments in diameter,i.e., equal steps from one end to the other. Also, the steps on theother conductor assembly are preferably of equal increments. In thepreferred embodiment, the equal steps on one conductor correspond to thesteps on the other in number and are slightly axially displaced relativeto each other.

For example, each step may differ from the adjacent step by a change indiameter of 0.2 inch. In the instance of the outer conductor assembly,the cylindrical steps may have diameters of 3.4, 3.2, 3.0 and 2.8inches, progressing toward the smaller coaxial line. Similarly, theinner conductor may have diameters of 0.9, 0.7, 0.5 and 0.3 inch, thesteps of one series being substantially equal in axial length to thecorresponding steps in the other series. Advantageously, an insulatingsleeve encircles the smallest cylindrical section and projects beyondthe endwall a limited distance into the housing to define with theadjacent larger cylindrical section of inner conductor a Meinke step.

In accordance with other aspects of the invention, a connector sectionor coaxial line discontinuity is provided in which the outer connectorassembly is proivded with a frusto-conical inner surface which has amean slope in the range of 20-40 toward a first apex and the innerconnector assembly has a frustro-conical outer surface which tapersinwardly toward a second apex. In this particular embodiment, bothfrusto-conical surfaces taper along substantially parallel lines. Thisparallel relationship, however, is not critical. In the preferredembodiment for connecting a coaxial line to a line termination, thefrusto-conical inner conductor portion tapers to a iirst cylindricalsection having a diameter intermediate the diameter of the resistiveinner conductor and the inner conductor of the coaxial line. This firstcylindrical section is connected to a second cylindrical section thediameter of which is intermediate the diameter of the first cylindricalsection and the pin which connects and is substantially equal indiameter to the inner conductor of the coaxial line. The insulatingsleeve encircles this second cylindrical section and projects inwardlyinto the housing a relatively short distance to the first cylindricalsection to define with the second cylindrical section a Meinke step.

These and various other objects and features of the invention will bemore clearly understood from a reading of the detailed description ofthe invention in conjunction with the drawing in which:

FIGURE 1 is a fragmentary view in elevation, partly in section, of oneillustrative embodiment of this invention; and

FIGURE 2 is a fragmentary elevational view, partly in section, ofanother illustrative embodiment of this invention.

Referring now to the 4drawing one illustrative embodiment of thisinvention is shown in FIGURE 1 in which a line termination 10 includes algenerally cylindrical housing 11 having oppositely disposed endwalls12, 13, :ach secured to the housing 11 in fluid sealing relation- ;hipas will be subsequently described in detail. The housng 11 supports laplurality of radiating fins 14, only a few of which are shown for thesake of simplicity. A pair 3f Z-shaped feet 15 are secured to the lowerportion of :he housing 11 as by Welding to support the housing 11.

The end wall 12 is secured to the housing 11 by a clampng ring 16 whichis generally V-shaped in cross-section 1nd is securely held in positionby a screw, not shown, which engages depending ears of the rin-g, alsonot shown. l`he clamping ring 16 engages a depending flange 17 of ;hehousing 11 and also the edge of the endwall 12. The :ndwall 12 isprovided with a recessed Ovring 18 which Jrevents the escape of thecooling dielectric fluid, not ihown, which substantially fills thehousing 11.

A. coaxial connector 19 is mouned on endwall 12 for he purpose ofconnecting a coaxial line heat dissipating ermination 20 within thehousing 11 to a coaxial line 51, shown in dotted outline. The coaxialconnector 19 nay be of the type shown in Bird et al. Patent 2,966,- 545,issued Dec. 27, 1960 or it may be any other suittble type well known inthe art. In this particular eximple, however, the connectorsubstantially corresponds o the connector shown in FIGURE 3 of the abovemenioned Bird et al. Patent.

The heat dissipating line termination 20 includes an uter conductor 22which is horn-shaped and which tap- :rs inwardly and is connected to acylindrical resistive nner conductor 23 by means of a clamp 24 and aclampng screw 25. The line termination 20 is generally of the ype shownin Bird et al. Patent 3,158,823, issued Nov. 24, .964.

The line termination 20 is mounted on and connected o the endwall 12 bymeans of a novel nonreecting conlector section according to oneillustrative e-mbodinent of this invention. The line connector section30 ncludes an outer connector assembly 31 which is se- :ured to acylindrical projection 32 of the endwall 12 y means of suitable screwssuch as screw 33. The outer `onnector assembly 31 includes a sleeveportion 34 which xtends over the screw 33 and extends within thecylinlrical portion of the outer conductor 22.

Advantageously the cylindrical outer connector section 1 has an innersurface which contains a first series of :ylindrical steps 38, 39, and41 which are of pro- ;ressively decreasing diameter, in the direction ofthe oaxial line 21. Preferably, the apices of each of these `ylindricalsteps is positioned on a sraight line 42 which epresents the mean slopeof the inner surface and makes ,n angle of 'at least 20 with the axis ofthe coaxial lfne nd the coincident axis of inner conductor 23. In thepreerred embodiment, the angle which line 42 makes with he axis 43 is atleast 26, is in the range of 26-40 .nd in one particular instance was261/2 The novel con- .ector section 30 also includes an inner connectorsecion 45 which contains a slotted sleeve portion 46 for nugly engagingthe periphery of the terminal of the reistive inner conductor 23 in goodelectrical conducting elationship in a manner well known in the art. Theinner onnector section 45 also includes a series of cylindrical teps 47,48, 49 and 50 which are of progressively dereasing diameter in thedirection of the coaxial line 21. `he smallest cylindrical section 50has a bore 52 on the nterior thereof to receive a connector pin 53 ofthe co- `xial connector 19 in a manner well known in the art.ldvantageously, the apices of the cylindrical steps 47, 8 and 49 lie ona substantially straight line 54 which lakes an agle with the coaxialline axis 43, which angle i substantially equal to the angle formed bythe line 42 :rough the apices of the steps on the outer connector ection31. In other words, the line 54 is substantially arallel to the line 42.

In accordance with an important feature of the invenon, an insulatingsleeve 55 encircles the cylindrical section 50. Sleeve 55 includes areduced cylindrical portion 56 lying entirely within endwall 12 and alarger diameter cylindrical portion 57 which projects slightly into theinterior of the housing 11. The projecting segment of sleeve portion 57and the cylindrical section 50 comprise a Meinke Step which is a wellknown form 0f coaxial line discontinuity. For best results theprojecting segment should not project beyond the endwall 12 more than.250. Also, the portion 57 of sleeve 55 should have a diameter greaterthan the dia-meter of section 49. In this particular embodiment, thediameter of section 57 is approximately equal to the diameter of innerconnector section 47. The diameter of section 56 is substantially equalto that of connector section 48. The cylindrical steps of progressivelydecreasing diameter on the inner conductor 45 and on the outer connectorsection 31 are easy to machine and are therefore preferred fro-m theeconomy standpoint. Further, because of their relatively short axialdimension the inner and outer connector sections 45 and 31,respectively, provide for coupling between the coaxial line 21 and theline termination 20 within a relatively short axial dimension regardlessof the large differences in diameters. Because of their peculiarelectrical characteristics, the connector section 30 provides relativelylow reflection while coupling coaxial sections which vary widely indiameter ratios. In one particular illustrative embodiment the diameterratios are of the order of 10-1 and provide for good electrical transferof energy in a range measured up to 3 kmc. with a voltage standing waveratio which was less than 1.38.

Another illustrative embodiment of connector section is shown in FIGURE2 for connecting the line termination 20 to the coaxial connector 19. Inthis particular embodiment, a connector section 60 is employed, whichconnector section includes an outer connector assembly 61 having afrusto-conical inner surface 62, a sleeve member 63 which encircles themember y61 and receives the cylindrical portion of the horn-shaped outerconductor 22, and an inner connector element `64 having a frusto-conicalouter surface 65 which connects a slotted sleeve section 66 to a firstreduced cylindrical section 67, intermediate in diameter to the diameterto the cylindrical sleeve section 66 and a second cylindrical section68. The reduced cylindrical section 68 has a bore on the interior toreceive the connector pin of the coaxial connector 19 in a mannersimilar to that of section 50 of FIGURE 1. Also, the insulating sleeve55 of FIGURE 1 is employed in the embodiment of FIGURE 2 with section 57projecting a relatively short distance into the interior housing 11, notshown in FIGURE 2. The section 57 preferably projects less than .250beyond the endwall 12 and cooperates with cylindrical inner conductorsection 68 to define a Meinke step. The outside diameter of section 57is less 'than the outer diameter of resistor 23 and greater than thediameter of section 72. The diameter of section 56 of sleeve 55 isgreater than the diameter of inner conductor section 72 and less thanthe diameter of section 57.

Advantageously the frusto-conical surface 62 tapers along a line 70 atan angle of the order of 26 and in the particular example illustrated is26%". The frusto-conical surface 65 on the inner connector assembly 64preferably tapers along a line 72 substantially parallel to the line 70In this particular example the line 72 forms an angle of approxiamtely25 with the axis of the coaxial line termination 20. The assembly ofFIGURE 2 constitutes an irnproved embodiment relative to the firstembodiment shown in FIGURE 1 from the electrical standpoint. However,the embodiment of FIGURE 2 is more difficult to machine and thereforemore expensive. The embodiment in FIGURE 2 constitutes an arrangementfor producing a compensated discontinuity or coupling section which isrelatively short and offers a minimum of reflection between coaxial linesections of a coaxial line section and a coaxial device where thediameter ratios are relatively large.

While two illustrative embodiments have beed described in detail, it isunderstood that the concepts thereof could be employed in otherembodiments without departing from the spirit and scope of thisinvention. For example, while the mean slope of line 42 relative to axis43 of FIG- URE 1 and line 70 relative to 71 are substantially the same,i.e., 261/2 it is understood that suitable results are obtained if themean slope exceeds 20 and is less than 40. The number of steps in theembodiment of FIGURE 1 on the inner connector element 4S should besubstantially equal to and slightly displaced from the correspondingsteps 38 through 41 on the outer connector assembly 31.

The term mean slope means the effective slope of a line through theprojecting apices of a plurality of steps or the slope of a smooth wall,both relative to the axis of the inner conductor.

I claim:

1. A couplig device for connecting a coaxial line to a coaxial linetermination having front and rear ends, and having a voltage standingwave ratio less than 1.38 for frequencies up to 3 kilomegacycles, anouter elongated circular sectioned sleeve conductor tapering inwardlyfrom a relatively large diameter at its front end to a relatively smalldiameter at its rear end, a resistor coaxially mounted within andgenerally spaced from said sleeve, one end of said resistor beingelectrically connected to the rear end of said sleeve conductor and afluid tight housing enclosing said line section, including an endwallcornprising:

outer connector means adapted to connect said outer f conductor of saidcoaxial line to said sleeve conductor; and

inner connector means for connecting the other end of said resistor tothe inner conductor of said coaxial line, said outer connector meanshaving a section which has a mean slope toward the axis of said coaxialline in the range of between 20 and 40 and wherein said inner connectormeans includes at least two cylindrical sections of dilferent diametersand an annular insulating member encircling the smaller of said twocylindrical sections and having its major portion positioned within saidendwall and having a minor portion projecting beyond said endwall intosaid housing.

2. A coupling device for connecting a coaxial line to a coaxial linetermination having front and rear ends, and having a voltage standingwave ratio less than 1.38 for frequencies up to 3 kilomegacycles, anouter elongated circular sectioned sleeve conductor tapering inwardlyfrom a relatively large diameter at its rear end, a resistor coaxiallymounted within and generally spaced from said sleeve, one end of saidresistor being electrically connected to the rear end of said sleeveconductor and a lluid tight housing enclosing said line section,including an endwall comprising:

outer connector means adapted to connect said outer conductor of saidcoaxial line to said sleeve conductor; and

inner connector means for connecting the other end of said resistor tothe inner conductor of said coaxial line, said outer connector meanshaving a section which has a mean slope toward the axis of said coaxialline in the range of between 20 and 40 and wherein said inner connectormeans includes at least two cylindrical sections of different diametersand an annual insulating member encircling the smaller of said twocylindrical sections and having its major portion positioned within saidendwall and having a minor portion projecting beyond said endwall intosaid housing; said section of said outer connector means including aplurality of stepped cylindrical portions; said inner connector meanshaving the same number of stepped cylindrical sections as the number ofstepped cylindrical portions on said outer connector means.

3. A coaxial line discontinuity connecting a first coaxial line sectionto a second coaxial line section of larger diameter than said firstsection while exhibiting a voltage standing wave ratio less than 1.38for frequencies up to 3 kilomegacycles comprising:

outer conductor means connecting the outer conductors of said iirst andsecond line sections and having a series of right angle transitions onits inner surface wherein the apices of all of the right angles of theseries lie on a straight line, said straight line having a mean slope inthe range of between 20 and 40;

inner conductor means connecting the inner conductors of said rst andsecond line sections and having a second series of right angletransitions, and an insulating sleeve on one portion of said innerconductor means and dening therewith a Meinke step.

4. A discontinuity according to claim 3 wherein said mean slope is atleast 26.

References Cited UNITED STATES PATENTS 3,095,545 6/1963 Bird et al.333-22 2,793,352 5/1957 Bird 339-177 3,213,392 10/1965 Hedberg 333-1223,350,666 10/1967 Zeigler 333-33 3,296,560 1/ 1967 Calderhead 333--223,311,856 3/1967 Conney 333--22 2,968,774 1/1961 Rodriguez 333-22 HERMANKARL SAALBACH, Primary Examiner C. BARAFF, Assistant Examiner U.S. Cl.X.R.

